Oh how I wish I could go back in time to when I was 17. I would give anything to go back and tell my mom and step-dad they were in a cult, tell them why, drop mic and walk out. Then go to college and do what I really wanted to do with my life.
But as it was I didn't bother to finish high school because, why bother? The end of the world is coming at any second! (I would have graduated in 1984).
All I can say is have him figure out what he wants to do and go do it. At 17 he is the only one stopping himself.